Re: [PATCH v13 11/32] x86,fs/resctrl: Handle events that can be read from any CPU

[Chen, Yu C]

On 10/30/2025 11:54 PM, Luck, Tony wrote:
> On Thu, Oct 30, 2025 at 02:14:27PM +0800, Chen, Yu C wrote:
> > Hi Tony,
> >
> > On 10/30/2025 12:20 AM, Tony Luck wrote:
> > > resctrl assumes that monitor events can only be read from a CPU in the
> > > cpumask_t set of each domain.  This is true for x86 events accessed
> > > with an MSR interface, but may not be true for other access methods such
> > > as MMIO.
> > >
> > > Introduce and use flag mon_evt::any_cpu, settable by architecture, that
> > > indicates there are no restrictions on which CPU can read that event.
> > >
> > > Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> >
> > [snip]
> >
> > > -void resctrl_enable_mon_event(enum resctrl_event_id eventid)
> > > +void resctrl_enable_mon_event(enum resctrl_event_id eventid, bool any_cpu)
> > >    {
> > >    	if (WARN_ON_ONCE(eventid < QOS_FIRST_EVENT || eventid >= QOS_NUM_EVENTS))
> > >    		return;
> > > @@ -984,6 +984,7 @@ void resctrl_enable_mon_event(enum resctrl_event_id eventid)
> > >    		return;
> > >    	}
> > > +	mon_event_all[eventid].any_cpu = any_cpu;
> > >    	mon_event_all[eventid].enabled = true;
> > >    }
> >
> > It seems that cpu_on_correct_domain() was dropped, due to
> > the refactor of __mon_event_count() in patch 0006 means it is no
> > longer needed.  But we still invoke smp_processor_id() in preemptible
> > context in __l3_mon_event_count() before further checkings, which would
> > cause a warning.
> > [ 4266.361951] BUG: using smp_processor_id() in preemptible [00000000] code:
> > grep/1603
> > [ 4266.363231] caller is __l3_mon_event_count+0x30/0x2a0
> > [ 4266.364250] Call Trace:
> > [ 4266.364262]  <TASK>
> > [ 4266.364273]  dump_stack_lvl+0x53/0x70
> > [ 4266.364289]  check_preemption_disabled+0xca/0xe0
> > [ 4266.364303]  __l3_mon_event_count+0x30/0x2a0
> > [ 4266.364320]  mon_event_count+0x22/0x90
> > [ 4266.364334]  rdtgroup_mondata_show+0x108/0x390
> > [ 4266.364353]  seq_read_iter+0x10d/0x450
> > [ 4266.364368]  vfs_read+0x215/0x330
> > [ 4266.364386]  ksys_read+0x6b/0xe0
> > [ 4266.364401]  do_syscall_64+0x57/0xd70
>
> I didn't notice this in my testing. Is this in your region aware
> tree? If you are still using RDT_RESOURCE_L3 then I can see how
> you got this call trace.

Yes, it was tested on the region aware tree.

> Maybe you need to dig cpu_on_correct_domain() back up and apply
> it to __l3_mon_event_count()?

Got it, will do.

Thanks,
Chenyu